All timestamps are in UTC by default and are formatted according to
ISO 8601
standard.

YYYY-MM-DDTHH:MM:SSZ
e.g. 2018-05-24T17:52:41+00:00

You can change the timezone used for dates on the Account page or by using
the PUT timezone route, as described
here.

Additionally, you can change the timezone used for a single request by setting the
timezone parameter in that request. If the timezone is not
valid, it will default to the timezone stored in your account. You can view a list of valid
timezones here.
Note that any slash characters in the timezone should be URL-encoded.